The present invention generally relates to ink delivery systems, and more particularly to a thermal inkjet printhead which is characterized by improved reliability, increased longevity, diminished production costs, cooler printhead operating temperatures, and greater overall printing efficiency. These goals are accomplished through the use of one or more novel resistor elements located within the printhead which are produced from a specialized alloy composition as discussed in considerable detail below.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon [Si] and/or other comparable materials) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure that is conventionally characterized as a "printhead". Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. Nos. 4,500,895 to Buck et al.; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. Pat. No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
The ink delivery systems described above (and comparable printing units using thermal inkjet technology) typically include an ink containment unit (e.g. a housing, vessel, or tank) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is directly attached to the remaining components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be "on-board" as shown in, for example, U.S. Pat. No. 4,771,295 to Baker et al. However, in other cases, the ink containment unit will be provided at a remote location within the printer, with the ink containment unit being operatively connected to and in fluid communication with the printhead using one or more ink transfer conduits. These particular systems are conventionally known as "off-axis" printing units. Representative, non-limiting off-axis ink delivery systems are discussed in co-owned U.S. Pat. No. 6,158,853 to Olsen et al. and co-owned U.S. Pat. No. 5,975,686 to Hauck et al. which are each incorporated herein by reference. The present invention is applicable to both on-board and off-axis systems (as well as any other types which include at least one ink containment vessel that is either directly or remotely in fluid communication with a printhead containing at least one ink-ejecting resistor therein as will become readily apparent from the discussion provided below.)
Regardless of the particular ink delivery system being employed, an important factor to consider involves the operating efficiency of the printhead with particular reference to the resistor elements that are used to expel ink on-demand during printhead operation. The term "operating efficiency" shall encompass a number of different items including but not limited to internal temperature levels, ink delivery speed, expulsion frequency, energy requirements (e.g. current consumption), and the like. Typical and conventional resistor elements used for ink ejection in a thermal inkjet printhead are produced from a number of compositions including but not limited to a mixture of elemental tantalum [Ta] and elemental aluminum [Al] (also known as "TaAl"), as well as other comparable materials including tantalum nitride ("Ta.sub.2 N"). Standard ink delivery resistor systems are discussed in considerable detail in U.S. Pat. No. 4,535,343 to Wright et al.; U.S. Pat. No. 4,616,408 to Lloyd; and U.S. Pat. No. 5,122,812 to Hess et al. which are all incorporated herein by reference.
However, the chemical and physical characteristics of the resistor elements which are selected for use in a thermal inkjet printhead will directly influence the overall operating efficiency of the printhead. It is especially important that the resistor elements (and resistive materials associated therewith) be as energy efficient as possible and are capable of operating at low current levels. Resistive compounds having high current requirements are typically characterized by numerous disadvantages including a need for high cost, high-current power supplies in the printer unit under consideration. Likewise, additional losses of electrical efficiency can occur which are caused by the passage of greater current levels through the electrical "interconnect structures" (circuit traces, etc.) in the printhead that are attached to the resistor(s), with such interconnect structures exhibiting "parasitic resistances". These parasitic resistances cause increased energy losses as greater current levels pass therethrough, with such energy losses being reduced when current levels are diminished. Likewise, high current requirements in the resistor elements and the "parasitic resistances" mentioned above can result in (1) greater overall temperatures within the printhead (with particular reference to the substrate or "die" on which the printhead components are positioned [discussed further below]); and (2) lower printhead reliability/longevity levels.
While conventional resistor materials including TaAl and Ta.sub.2 N have functioned adequately in thermal inkjet printing systems of the types discussed above, the foregoing disadvantages are nonetheless an important consideration which leaves room for improvement. In this regard, a need remained (prior to development of the present invention) for a resistor system suitable for use in thermal inkjet printing systems of all types which is capable of high efficiency/low current operation. The present invention satisfies this need by providing novel resistor elements that represent a substantial improvement over prior resistor units. The resistor elements of the claimed invention specifically offer a number of advantages including but not limited to: (1) decreased current requirements which lead to improved electrical efficiency; (2) reductions in printhead operating temperatures with particular reference to the substrate or "die"; (3) the general promotion of more favorable temperature conditions within the printhead (which result from reduced current requirements that correspondingly decrease current-based parasitic heat losses from "interconnect structures" attached to the resistors); (4) multiple economic benefits including the ability to use less-costly, high voltage/low current power supplies; (5) improved overall reliability, stability, and longevity levels in connection with the printhead and resistor elements; (6) the avoidance of heating efficiency problems which can lead to resistor "hot spots", absolute limits on resistance, and the like; (7) greater "bulk resistivity" as defined below compared with conventional resistor materials such as TaAl and Ta.sub.2 N; (8) the ability to place more resistors within a given printhead in view of the reduced operating temperatures listed above; (9) a reduction in electromigration problems; and (10) generally superior long-term operating performance. As will become readily apparent from the discussion provided below, the novel materials selected for use in producing the claimed resistor elements offer these and other important benefits. The structures discussed herein therefore constitute a substantial advance in the art of thermal inkjet printhead design compared with prior (e.g. conventional) systems.
In accordance with the detailed information provided below, the present invention involves a thermal inkjet printhead having one or more novel resistor elements therein which are unique in structure, construction materials, and functional capability. Also encompassed within the invention is an ink delivery system using the claimed printhead and a manufacturing method for producing the printhead. Each of these developments will be outlined in considerable detail below. Accordingly, the present invention again represents a significant advance in thermal inkjet technology which ensures high levels of operating efficiency, excellent image quality, rapid throughput, and increased longevity which are important goals in any printing system.